Arizona State University 2D BEAM STEERING USING ELECTROSTATIC AND THERMAL ACTUATION FOR NETWORKED CONTROL Jitendra Makwana 1, Stephen Phillips 1, Lifeng Wang 1, Nathan Wedge 2, and Vincenzo Liberatore 2 1 Department of Electrical Engineering Arizona State University Tempe, Arizona 2 Department of Electrical Engineering and Computer Science Case Western Reserve University Cleveland, Ohio

Arizona State University OUTLINE u Networked Control Systems u NCS and MEMS u Example Testbed u Beam Steering Actuator u Modelling and Proposed Fabrication u Simulated Performance u Conclusion and Future Work

Arizona State University Feedback Control u Traditional feedback –Multiple sensors/actuators –Dedicated channels with deterministic delays –Predictable performance without failures –Robust to physical system variations Physical System Controller A S

Arizona State University Networked Control System (NCS) u NCS feedback –Reconfigurable structure –Communication with nondeterministic delays –Robust to communication failures

Arizona State University NCS and MEMS u In MEMS –NCS enables operation distant from its control –Complex control strategies achieved by leveraging remote computational power –Extends the capability of an integrated MEMS device –Beam steering device as actuator for NCS testbed –One example testbed involves a mobile agents performing laser tracking

Arizona State University Battlefield Application u Steered Beam –Secure communications –Resource tracking –Target tracking –Robust to obstacles, node failures, communication failures

Arizona State University Actuator and Sensor u Implementation –2DoF Tilting mirror actuator –Measured beam position sensor

Arizona State University REQUIREMENTS u For a beam steering actuator –2 Degrees of freedom –Low power consumption/dissipation –Low voltage for electrostatic actuation –Low current for thermal actuation –Fast steering capabilities –Adequate tilt angle

Arizona State University ELECTROSTATIC ACTUATION u Zipper actuator top view –Large deflections at low voltages –Four cantilever beams –Two springs per beam –Mirror MIRROR SPRING CANTILEVER BEAM

Arizona State University ELECTROSTATIC ACTUATION u Zipper actuator side view –Sputtered aluminum for structure, conductivity, reflectivity –Anti-reflective coating (ARC) allows for only mirror reflectivity –Sacrificial Oxide for air-gap between the top and bottom plates –Silicon nitride (SiN) prevents top and bottom plate shorting SPRINGAMORPHOUS SILICON ALUMINUM NITRIDEGAP, g LENGTH, L1 LENGTH, L LENGTH, L2 MIRROR ARC

Arizona State University ELECTROSTATIC ACTUATION u Zipper actuator side view –Mirror held by beams through springs –Beams at ground potential –Bottom plates positive actuation voltage SPRINGAMORPHOUS SILICON ALUMINUM NITRIDEGAP, g LENGTH, L1 LENGTH, L LENGTH, L2 MIRROR ARC

Arizona State University ELECTROSTATIC ACTUATION u Zipper actuator after release: Simulated –Al vs. a-Si coefficients of thermal expansion –Beams bend upwards –Mirror elevation is 25  m D D D D Max. stress at supports D is 43 MPa Max. stress in springs is 60 MPa

Arizona State University ELECTROSTATIC ACTUATION u Zipper actuator design and model F e : Electrostatic force V : Voltage applied W : Width of cantilever beam = 100  m H : Top electrode thickness = 0.5  m g : Air gap = 1  m x def = Cantilever beam deflection

Arizona State University ELECTROSTATIC ACTUATION u Zipper actuator design and model - Electric field x def = 8.75  m for 5 o tilt L2 = Mirror length = 100  m θ =

Arizona State University ELECTROSTATIC ACTUATION u Zipper actuator design and model F e = F b F b : Cantilever beam force = k c x def L = Mirror length = 505  m k c : Composite cantilever beam spring constant = 146 x N/  m E eq : 94 GPa (from simulation)

Arizona State University ELECTROSTATIC ACTUATION u vs. V: Simulated θ

Arizona State University ELECTROSTATIC ACTUATION u Gap much less than beam width  Squeeze-film damping effects are dominant. The quality factor and the damping coefficient are:

Arizona State University ELECTROSTATIC ACTUATION u Zipper actuator switching capability - Rise time (t r ) and Settling time (t s ) for a second order system is given by D D ω n ≈ ω d =2.5×10 4 rad/s (simulation)

Arizona State University ELECTROSTATIC ACTUATION u Zipper actuator tilt: Simulated Room temperature D Max. stress at supports D is 130 MPa Max. stress at springs is 500 MPa Rise time 63  s Settling time 702  s D D D D

Arizona State University THERMAL ACTUATION u Thermal actuator side view –Al and SiN multilayer cantilever beams –Joule heating in serpentine top layer –Nitride layer used for thermal insulation SPRING SILICON NITRIDEALUMINUM GAP, g LENGTH, L LENGTH, L2 MIRROR

Arizona State University THERMAL ACTUATION u Thermal actuator side view –Top Al is much thinner than bottom Al layer –Release at room temperature, all beams bend upwards –Similar to electrostatic zipper actuator SPRING SILICON NITRIDEALUMINUM GAP, g LENGTH, L LENGTH, L2 MIRROR

Arizona State University THERMAL ACTUATION u Thermal actuator thermal energy –Heat energy (J) required to heat  m = Density of aluminum = 2700 kg/m 3 a = Aluminum thickness of serpentine = 0.1  m W = Aluminum width of serpentine = 15  m L = Aluminum length of serpentine= 3.64 x 10 3  m C m = Specific heat per unit mass for aluminum = 900 J/(kg-K)

Arizona State University THERMAL ACTUATION u Thermal actuator heating/power dissipation

Arizona State University THERMAL ACTUATION  T = T K Max. stress at supports D is 300 MPa Max. stress at springs is 230 MPa D D D D

Arizona State University THERMAL ACTUATION u Time (t) required to heat resistor at 1  A of current using voltage variable source

Arizona State University THERMAL ACTUATION

Arizona State University SUMMARY u Beam steering using electrostatic, thermal actuation. u Four cantilever beams with spring suspended mirror u Electrostatic tilt angle of 5 o at 43 V. u Electrostatic actuator t r and t s are 63  s and 702  s u Thermal actuator  T = 60 K for 5 o tilt in 10 ms. u Fabrication in progress u NSF funding through grant CCR